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Animal control systems are well-known. Examples of such a system are found in U.S. Pat. No. 5,465,687 and U.S. Pat. No. 5,353,744, both assigned to the assignee of the present invention and incorporated herein by reference. A transmitter generates a coded Amplitude Modulation (AM) signal that is radiated by a wire-loop antenna which is buried a few inches underground and defines an area within which the animal is to be contained or from which the animal is to be restricted. A receiver mounted on a collar placed around the neck of the animal includes one or more electrodes which are in physical contact with the skin of the animal. As the animal and receiver approach the wire-loop antenna, the receiver detects the radiated AM signal. The received signal is measured and, if the received signal qualifies, that is, meets certain criteria, a stimulus is applied to the animal. The stimulus may be an audible alert and/or an electric shock administered to the animal through the electrodes.
In accordance with the invention, an animal control system is provided in which an AM transmission signal includes qualification criteria which upon proper decoding provides intended stimuli to an animal. The transmit signal comprises modulated pulses having a first amplitude and a second amplitude which upon decoding represent logic zero and logic one states. The receiver employs microprocessor based digital circuitry for decoding and processing of the AM transmit signal. The transmit signal is transmitted in alternating odd and even frames, each of which has particular characteristics.
The qualification protocol operates as follows. A detected signal above a predetermined threshold level is deemed a qualified signal. Upon detection of a first qualified signal during a first frame, a weak stimuli command is produced. Upon detection of a second qualified signal during a second frame immediately following the first frame, a strong stimuli command is provided. The detection routine continues for subsequent odd and even frames so long as qualified signals are detected. Thus, alternating weak and strong stimuli commands are provided to produce corresponding weak and strong stimuli to the animal. The weak stimuli are in the form of a sound of relatively low intensity and a shock of relatively low intensity. The strong stimuli are composed of a louder sound and stronger shock pulse.
In an alternative mode of operation, the stimuli can be solely auditory with no shock provided to the animal in this mode.
The gain of the received signal is tested against the threshold level by use of a variable gain amplifier, the gain of which is reduced by a predetermined amount, typically by about 8%, and comparison of the reduced gain signal with the predetermined threshold. If the reduced gain signal is above the threshold, the signal is qualified. If the signal is not at or above the threshold level, the signal is not qualified and decoding is discontinued. The reduction in the gain during the signal qualification process assures that the qualified signal is well above the threshold level for subsequent processing to occur.